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How does this circuit work?

DougB

Oct 13, 2012
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Could you post in-focus photos of both sides the board with good illumination on it? If possible illuminate it at a slight angle and photograph it straight so the photo has no reflection of the light source.


I've attached the best pics I could get. I took a pic of both ends of the boards on the component side and the circuit side. The first pic shows the the two sides of the component side stitched as best as I could and annotated, showing the rough path path the connector to the micro. The other are the raw pics. Hope this is what you want. If you need higher resolution than they allow here, send me a PM with your email address.

Thanks for your effort!

Doug
 

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KrisBlueNZ

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Thanks for the photos. They look good.

Well, you COULD replace the micro if you want. The firmware is in the separate EPROM; the micro is not programmed internally. But as you say, that would be a big job.

Where are the connectors? The only one I see is the phone jack. Does everything go through that?

Where is the power supply? Is there another board we need to look at? What's at the other end of the RJ-45 cable?

If everything goes through that RJ45 connector, you might want to check continuity from pin to pin of the socket on that board and the socket on the other board. Cables and modular connectors can have problems; it could just be a disconnected or insufficiently crimped wire.
 

DougB

Oct 13, 2012
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Where are the connectors? The only one I see is the phone jack. Does everything go through that?

Where is the power supply? Is there another board we need to look at? What's at the other end of the RJ-45 cable?

If everything goes through that RJ45 connector, you might want to check continuity from pin to pin of the socket on that board and the socket on the other board. Cables and modular connectors can have problems; it could just be a disconnected or insufficiently crimped wire.

Attached is the power board. The RJ-45 cable connects the two - power is supplied to the display board. I have checked the continuity of the trace in question, but not all of them. I'll check them.
 

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KrisBlueNZ

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Can you post the underside as well? And those pics are a bit out of focus and there's a reflection on the west one so that I can't see the markings on U5.

I also noticed two resistors that seem to have burnt up, marked R13 and R14. What's the story with those?
 

DougB

Oct 13, 2012
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I also noticed two resistors that seem to have burnt up, marked R13 and R14. What's the story with those?

Good eye!! I think that just happened when I grounded Pin 16 of the micro. I thought I saw a little smoke! Either that, or every time I make the motor go by influencing the gate on the VN2222, it scorches it a little more. I suspect it's the former for some reason. When I grounded it, if I don't shut off the power immediately, I think it continuously draws power even though the micro has presented the error and shuts off the motor.........Oh, that's interesting - how does the micro shut off the motor when I'm forcing the motor through the VN2222........ My schematic has errors in that area, so if you need that detailed better, let me know. Otherwise the resistors are in the circuit that goes to the Crydom gates. In any case, I'm in trouble now because the ID bands are scorched. I can see that the first and second are red then green and the last is gold, but the multiplier band is not readable. When I remove it and measure the resistance, it measures 1.5K on both. Do you think I can assume they were 2.5K????

Better pictures are attached.
 

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KrisBlueNZ

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Thanks for the pics Doug, I'll have a look at them soon.

Re the micro turning off the motor, I think it controls the motor through an electromechanical (standard) relay as well as the Crydom solid state relay. The electromechanical relay is used for on/off control, and the solid state relay is turned on and off at different parts of the mains cycle to control the speed. That's what I think from your original schematic.

Re the resistors, do they look like they were identical? Is it possible that the first band was originally brown but now looks more like red? 2.5K is not a preferred value, but 1.5K is. My guess is that they're 1.5K as you measured.

Did you check for continuity from one socket to the other between the boards on all connections?

Also it might be helpful to know the voltages on all the pins when the treadmill is powered up but idle.
 

KrisBlueNZ

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Doug, I think the mains zero-crossing detection is done by optocoupler U1, which is driven directly from the transformer secondary. Its output is on the track that goes to R2. This signal then goes off to the 74C14 but I can't follow it very well on the photo. Also, it seems to connect to the sensor at the edge of the board. I assume this sensor detects rotation of the flywheel, is that right? It shouldn't have anything to do with the mains signal.

Can you trace that part of the circuit from U1 output through the 74C14 and up to the modular jack connector? You can also check the voltage on the output pin of the 74C14 (once you figure out which pin it is) - it should measure about half of the 74C14's power supply voltage if the mains zero-crossing is working.
 

DougB

Oct 13, 2012
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it seems to connect to the sensor at the edge of the board. I assume this sensor detects rotation of the flywheel, is that right? It shouldn't have anything to do with the mains signal.

Yes , the sensor looks at black and white 'stripes' on the flywheel.


Can you trace that part of the circuit from U1 output through the 74C14 and up to the modular jack connector? You can also check the voltage on the output pin of the 74C14 (once you figure out which pin it is) - it should measure about half of the 74C14's power supply voltage if the mains zero-crossing is working.

See the new schematics below. Sorry for the handwriting, but I haven't found an easy (and free) circuit drawing package. The voltages are noted on the drawing. I didn't understand how the 74HC74 works, so I'll have to leave that to you. If you need more details, just give me more homework!

I thought I found the problem when I traced out that part of the circuit. There was a run that had been abraded that I had seen before but thought was OK. Since it was in the interest area, I jumped it, but no different operation.

I also check the continuity of the RJ-45 connector - all is well.

Thanks for your time.

Doug
 

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KrisBlueNZ

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Thanks for that Doug.

The mains waveform is detected by optocoupler U1. Input is at the bottom (on your drawing and on the photo) and output is on the top left pin, which is pulled up to the 5V VCC rail (which comes from the 5V regulator) by R2. This pin will normally sit at about half of VCC, or 2.5V. It feeds the IC that you've marked as U14, on pin 9.

U14 (or at least, the IC that the signal feeds into, at the top right of the board) is a 74C14 or CD40106 (actually it's both; they're different names for the same component). It's not a flip-flop; it's a hex inverter with Schmitt trigger inputs. It contains six inverter sections. Each inverter takes an input signal and produces an output signal that is the opposite logic state of its input, i.e. it inverts the signal. When the input is low, it will drive the output high, and vice versa.

One of these inverters has its input on pin 9 and its output on pin 8, which connects to the modular connector. This signal is the one the microcontroller uses to detect when the mains voltage crosses zero. It uses this timing information to control the conduction angle of the Crydom solid state relay, to vary the motor speed.

The voltages on pin 9 (inverter input) and 8 (inverter output) are 0.41V and 1.76V. This is not consistent. If the input measures 0.41V, then the output should measure 5-0.41V or 4.59V.

I think the 74C14 has been damaged, possibly by a voltage surge or electrostatic discharge (ESD), possibly involving the interconnect cable. I think if you replace it, you will fix the problem.
 

DougB

Oct 13, 2012
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U14 (or at least, the IC that the signal feeds into, at the top right of the board) is a 74C14 or CD40106 (actually it's both; they're different names for the same component). It's not a flip-flop; it's a hex inverter with Schmitt trigger inputs. It contains six inverter sections. Each inverter takes an input signal and produces an output signal that is the opposite logic state of its input, i.e. it inverts the signal. When the input is low, it will drive the output high, and vice versa.

Sorry, I labeled the IC wrong - it's U4. You are correct about it's component number.

I have ordered one today. I've got my fingers crossed! I'll let you know whenever I get it - it may be more than a week with our holiday coming next week.

Muchas Gracias!
 

DougB

Oct 13, 2012
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My fingers are crossed too :)

I guess we should have had our toes crossed too........replacing the CD40106 didn't work. Some of the voltages changed, but not the operation. Note that before, I was measuring VDC on pin 9 and 8. I guess I should have been measuring VAC? Pin 8 changed from VDC of 1.76 to VDC of 3.61, but I don't know what the VAC readings were. Now VAC9 is .5 and VAC8 is 7.1.

Well, have you run out of ideas yet??? If you have any, I'd sure like to hear them. You've put in a heroic effort so far - Thanks for that.
 

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KrisBlueNZ

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Bummer. Sorry about that. The 40106 looked like a very likely culprit.

You should be measuring VDC. The signals are AC, but measuring the DC voltage gives us the average voltage, which should be about half the supply voltage, since the signal should have a duty cycle of about 50%, i.e. it should be high about half the time. Since the supply voltage is 5V, pin 8 should be about 2.5V DC. The new voltage of 3.61 VDC is about as wrong as the old voltage of 1.76 VDC.

What's the DC voltage on pin 9 now? Also can you check that there's 5V on pin 14 of the 40106.

It would really help to see the waveforms on the 40106... Could you borrow an oscilloscope?

Also, I noticed there seems to be some pretty thick dirt or dust on the board. I guess it's possible that there's a leakage path across the optocoupler that could be affecting the 40106 or could even have damaged it. Ideally, I would remove all the components, scrub the board with isopropyl alcohol on both sides, then refit all the components, but that's quite a job. You could remove the optocoupler and clean the board in that area, and the optocoupler, though.

Can you also measure DC voltage on pins 9 and 8 of the 40106 with pins 1 and 2 of the optocoupler shorted together. Shorting the pins won't damage anything because R3 will limit the current.
 

DougB

Oct 13, 2012
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.

What's the DC voltage on pin 9 now? Also can you check that there's 5V on pin 14 of the 40106.
VDC pin 9 is .40 after removing the optocoupler and cleaning the board. There is 4.96 VDC on pin 14.

.
It would really help to see the waveforms on the 40106... Could you borrow an oscilloscope?

Sadly, no. I've looked at getting one, but it seems I'd have to spend at least $200USD to get a good enough one.


.
Can you also measure DC voltage on pins 9 and 8 of the 40106 with pins 1 and 2 of the optocoupler shorted together. Shorting the pins won't damage anything because R3 will limit the current.

With Pins 2 and 3 shorted, pin 9 is 4.93 VDC, and pin 8 is 0 VDC.
 

KrisBlueNZ

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OK, those voltages could be consistent if the optocoupler is an AC-input type that activates on both positive and negative voltages. In that case, a pin 9 voltage of 0.4 could be right, but pin 8 should be around 4.5V, not 3.61V.

What are the markings on the optocoupler?

The track from pin 8 of the 40106 goes past some high-voltage stuff. Is it possible that dirt on the board has caused the insulation to break down? Can you follow that track and clean the board in any areas where it runs close to anything live?

Can you measure the voltage on pin 8 of the 40106 with the modular connector unplugged. It's possible that the circuitry on the other end has been damaged and is pulling the voltage down.

Can you have a look at the circuitry on the control board that connects to the signal from pin 8 of the 40106. I guess eventually it goes into a pin of the micro but I hope there's some protection circuitry on it.

I gotta say, it's a nice change to get answers to all my questions. Usually on the forums, when we ask a series of questions, we might get an answer to one or two, if we're lucky.
 

DougB

Oct 13, 2012
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What are the markings on the optocoupler?
Looks like TIL 194.

The track from pin 8 of the 40106 goes past some high-voltage stuff. Is it possible that dirt on the board has caused the insulation to break down? Can you follow that track and clean the board in any areas where it runs close to anything live?
The track is pretty straightforward with no gunk that I see. It's pretty much insulated from others by a trace that encircles the trace coming from Pin 12 (some sort of shield).

Can you measure the voltage on pin 8 of the 40106 with the modular connector unplugged.

With the mod con disconnected: 4.68VDC

Can you have a look at the circuitry on the control board that connects to the signal from pin 8 of the 40106. I guess eventually it goes into a pin of the micro but I hope there's some protection circuitry on it.
See display board circuit schematic. That is the trace that I said had an abrasion on it and I added a wire to bypass it. That bypass is still on. The circuitry goes to U14 which is the flip flop I was confused about before and then to the micro . I don't understand the circuitry within U14(74HC74) so you may want to look at that . Also, that circuit goes through R25, then to U15, etc. Should I disconnect R25 to see if the stuff downstream is causing Pin 8 of the 40106 to be lower?

I gotta say, it's a nice change to get answers to all my questions. Usually on the forums, when we ask a series of questions, we might get an answer to one or two, if we're lucky.
Well, you're spending a lot of time on this, so I want to give you what you need!
 

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KrisBlueNZ

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(optocoupler)
Looks like TIL 194.
OK that makes sense. The TIL194 has bidirectional input. So the 0.4V you get on pin 9 of the 40106 is OK.
(track from 40106 pin 8 to modular connector)
The track is pretty straightforward with no gunk that I see. It's pretty much insulated from others by a trace that encircles the trace coming from Pin 12 (some sort of shield).
OK, no problem.
(40106 pin 8 voltage with modular connector unplugged)
With the mod con disconnected: 4.68VDC
Aha! That signal must be being loaded down by something on the main board.
(Circuitry connected to that signal on the main board)
See display board circuit schematic. That is the trace that I said had an abrasion on it and I added a wire to bypass it. That bypass is still on. The circuitry goes to U14 which is the flip flop I was confused about before and then to the micro . I don't understand the circuitry within U14(74HC74) so you may want to look at that . Also, that circuit goes through R25, then to U15, etc. Should I disconnect R25 to see if the stuff downstream is causing Pin 8 of the 40106 to be lower?
I'm not sure what you're saying about where that signal goes. Is it the track that feeds to Q6 via R26, with R25 to ground? If so, I doubt the problem will be with those components. There is something that's connected directly to that track that has been damaged - presumably by whatever caused the scuffing that you mentioned. (Make sure the board can't get near any moving parts when the treadmill is reassembled.)
You wrote on your diagram that that track goes out of sight somewhere. Check for continuity from that track to each pin on any IC near where the track disappears. If you get continuity, that IC is probably #%@#ed as well. (BTW, the 40106 was damaged too, so replacing it wasn't entirely a waste of time.)
I can't tell much from the schematic you've drawn; it's too incomplete. If you don't find anything with your continuity test, you'll need to fill in more of the circuitry connected to that signal and repost it.
(Thorough answers)
Well, you're spending a lot of time on this, so I want to give you what you need!
I'm not spending very much time, but I know what you mean. You'd be surprised how many people on this forum don't seem to have that attitude. Some don't even try to be polite. So with you, it's a pleasure to help.
 

DougB

Oct 13, 2012
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**SUCCESS**

KrisBlueNZ:

WOW, we did it!! Since you thought something was loading Pin 8, I started disconnecting things to see where the voltage got better. I started with R26. With that disconnected, the reading was a good 4.68. Then I put that back and disconnected Q6 and the reading was good. While I had Q6 out (it is a VN2222), I just replaced it and YIKES, it worked after I buttoned it up. So a simple $.44 made the difference. Of course I spent $50 on the Crydon, but - it's fixed!

The only issue now is: I have no excuse for not using the treadmill!!

I can't thank you enough for your diagnosis. I was beyond my pay grade way back. Your wisdom and tenacity is much appreciated! It's just another reason why I have such warm feelings for New Zealand - the New Zealand people are the best!

Thanks again and best of luck.

Doug
 

KrisBlueNZ

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That's fantastic Doug! And thanks for the e-card, that was a nice touch.
I'm sorry that you're going to have to USE the treadmill now. I guess we should've seen that one coming :)
Thanks for your kind words. You have been a pleasure to work with on this project.
Best regards
Kris
 

(*steve*)

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Great job Kris & Doug.

I'm sorry that you're going to have to USE the treadmill now. I guess we should've seen that one coming :)

Hey Doug, ask Kris nicely and I'm sure he'll come up with a way to introduce a fault that's almost impossible to find! :D
 
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